Gas flow uniformity is a factor in electrostatic precipitator performance. Gas distribution systems control the gas flow uniformity to the electrostatic precipitator. Any dust which accumulates on the gas distribution system blocks gas access through the electrostatic precipitator and as a result retards gas flow. To maximize electrostatic precipitator performance then, it is desirable to minimize dust accumulation on a gas distribution system.
A gas distribution system includes a plenum through which flue gas is distributed to the electrostatic precipitator. The quantity of dust accumulation or particulate buildup on the gas distribution system is a function of the plenum construction, as well as the type of flue gas. That is, the plenum, in channeling flue gas to the electrostatic precipitator, typically gathers dust and consequently obstructs gas flow. The amount of dust is related to the configuration and position of the plenum.
While it is common practice, after a number of machine operation cycles, to attempt to clean the plenum of dust accumulation doing such entails machine downtime. Further, in some instances the particulates must be manually removed hence, a loss in overall process efficiency. Moreover, often times cleaning is ineffective in that dust resists removal and continues to inhibit gas flow.
Typically, gas distribution systems for electrostatic precipitators include a plenum which transmits particulate laden flue gas from a duct to an electrostatic precipitator. The duct is essentially vertically positioned and has a relatively narrow interior cross sectional area. Flue gas comes in through the narrow duct and is transferred to the electrostatic precipitator. The electrostatic precipitator is positioned in an essentially horizontal direction having its opening or gas inlet approximately perpendicular to the duct. The gas inlet presents a rather large opening, relative to the duct's cross sectional area, for receipt of incoming flue gas. The incoming flue gas must be made to shift its path flow direction toward the gas inlet.
Moreover, for uniform distribution to the electrostatic precipitator the gas must be dispersed evenly over the gas inlet area.
Accordingly, a plenum is typically employed which functions to redirect and distribute the flow of gas from the flue duct to the electrostatic precipitator. It is the plenum on which dust collects, blocking the flow of gas into the electrostatic precipitator. The plenum therefore, impacts the flow of gas as it enters the electrostatic precipitator.
Commonly, as discussed subsequently in detail with reference to FIG. 1, two distinct elements are positioned in the plenum for controlling the gas flow. First, to direct the flue gas path line toward the electrostatic precipitator and avoid flue gas packing in the vertically lower-most corner of the plenum, it has been the conventional practice to place gas vanes in the interior of the plenum. Second, to distribute the gas, once redirected, across the electrostatic precipitator inlet, it has been the conventional practice to vertically extend across the plenum a flat perforated plate at the inlet location.
FIG. 1 shows a cross sectional view of a conventional electrostatic precipitator having gas distribution system 8. Here gas is input in the general direction of Arrow A through duct 10 into plenum 12 for distribution to electrostatic precipitator 14. The electrostatic precipitator then places a negative charge on gas particulates which in turn are attracted to positively charged collection plates 16. Thereafter, clean gas is expelled in the general direction of Arrow B.
As is seen in FIG. 1, it has been the common practice to utilize a ladder vane assembly 18. The ladder vane is formed by a series of near horizontal vanes and is positioned at an angle, relative to the electrostatic precipitator, across the width of plenum 12. The ladder vane shifts the initial gas path line from the general direction of Arrow A towards the horizontally positioned electrostatic precipitator 14 or the general direction of Arrow B. The ladder vane 18 includes spaced rungs 18a which extend between supports 18b. Spaced rungs 18a form a gap 18c through which the flue gas travels. More particularly, incoming flue gas following the gas path depicted by Arrow A, upon contacting the plenum sidewall 12a is turned towards the direction of ladder vane 18 and thereafter, upon encountering rungs 18a, rebounds through gap 18c towards the electrostatic precipitator gas inlet.
Moreover, if only the ladder vane 18 was employed in the plenum, the gas would accumulate or pack in the lower-most corner C of plenum 12 as a result of the directional angle it assumes after entry through the ladder vane. This would obstruct uniform gas flow thereby inhibiting electrostatic precipitator performance. Thus, to spread the gas across the electrostatic precipitator gas inlet 14c it has been the practice to position a perforated plate 20 across plenum 12 at the electrostatic precipitator gas inlet location. The plate being perforated presents both gas obstruction areas and open regions for gas travel. The gas upon encountering both obstruction areas and open regions naturally gravitates toward the open regions thus effecting a spreading of gas across the perforated plate expanse.
Unfortunately, the conventional plenum construction has proven unsatisfactory in operation for a number of reasons. The commonly used two part system is costly in that it requires the installation of two separate elements in the plenum, the ladder vane assembly and the perforated plate. Further, in the conventional ladder vane construction frequently salt cake particulate buildup occurs. This build up impedes gas flow and is difficult to remove.
The present invention provides a one piece gas distribution structure namely, a corrugated, perforated plate provided in the plenum. The corrugated, perforated plate performs the same functions of the conventional two part ladder vane and perforated plated assembly, that is, gas turning and spreading in an improved manner.
The corrugated, perforated plate construction of the present invention limits dust accumulation for at least three reasons. In the present invention the ladder vane is eliminated, thus, dust accumulation thereon is avoided. In contrast to the conventional system the plate of the present invention is able to maintain good reliable gas flow quality across the gas inlet region, accordingly little dust actually gathers on the corrugated, perforated plate. When particulates do buildup on the corrugated perforated plate, the present invention provides a simple and efficient rapping mechanism for the ready removal of dust.
That is, while the conventional distribution structure requires the manual cleaning of the ladder vane assembly, the corrugated, perforated plate of the present invention can be readily cleaned. In the present invention, the corrugated, perforated plate is hung on pipes suspended from the plenum, which when vigorously rapped, vibrate and force dust accumulation into the electrostatic precipitator hoppers.
For the above reasons relatively stable flow quality can be maintained over a number of machine operations. Indeed, tests have demonstrated that the present invention in operation produces a good reliable flow quality. Indeed, the corrugated, perforated plate exhibits a 19.62% RMS velocity index which remains relatively constant, in contrast to the conventional system, during machine operations despite repeated cleanings.
The advantages of the present invention are set forth in part in the following description, and will be obvious from the description or may be learned by practice of the invention. The advantages of the present invention may be realized and attained by means of the instrumentalities and combinations pointed out in the appended claims.